Synechococcus sp.

Class: Cyanophyceae
More of a generalist, Synechococcus are often less abundant than Prochlorococcus in regions where they coexist, but they are overall a more widespread cyanobacteria. They can be found in coastal waters and some are mixotrophic while others are capable of nitrogen fixation (although this particular strain is not)1. Cyanobacteria are key components of marine phytoplankton, especially in oligotrophic regions where they are often found to be the main primary producers. Cells are 1-2 um in diameter.
1Palenik B., B. Brahamsha, F. Larimer, M. Land, L. Hauser, P. Chain, J. Lamerdin, W. Regala, E.A. Allen, J. McCarren, I. Paulsen, A. Dufresne, F. Partensky, E. Webb, and J. Waterbury (2003). The genome of a motile marine Synechococcus. Nature 424: 1037-1042.